1. Field of the Invention
The invention relates to a production plant, in particular for folding workpieces to be produced from sheet metal, having an angle-measuring device, and a method for determining an angular position of at least one limb formed by a bending operation relative to a reference plane, as described in claims 1 and 12.
2. Description of the Related Art
From EP 0 637 371 B1 and the earlier document DE 694 11 821 T2, a device for measuring an angle on a workpiece is known, having feelers disposed in a base of the bending tool, which can be moved relative to the base. Each of the feelers has contact devices for contacting with the respective portion of the workpiece during the measurement, and the sensors are kinematically totally independent of one another. The device also has separate thrust mechanisms for moving the contact devices of the feelers into contact with the respective portions of the workpiece being measured. The thrust mechanisms co-operating with one feeler are totally independent of the thrust mechanisms co-operating with the other respective feeler. The thrust mechanism also enables the respective feeler to effect a movement in translation relative to the base totally independently of the movement of the other feeler. In addition, a sensor mechanism is provided, which is used to detect the position of the feelers relative to the base. To this end, each of the feelers has an active surface for establishing contact with the respective portion of the workpiece. The sensor mechanism in turn has a pair of distance-measuring elements, which are spaced apart from one another at a known distance and lie in a plane of the angle to be measured, and the measuring elements are connected to the displaceable feelers at two different points. Accordingly, a pair of these feelers and the connected measuring elements are disposed inside the base on which the workpiece is supported during the production process.
Bending angle measurements have also been taken in the past using digital image processing, distance sensors, light-slit sensors, feeler pins, measuring forks, rotatable die elements, contact plates or similar.
For the most part, these measuring devices are of a complicated design and are susceptible to faults to a large degree.